The use radio frequency devices, known as RFIDs has been increasingly widespread since such devices, or their equivalents (such as EAS devices) provide numerous practical advantages in a number of environments. As a result RFID devices have been incorporated in a wide variety of products, including labels and tags, such as shown in co-pending application Ser. Nos. 09/499,347 filed Feb. 8, 2000 and 09/393,291 filed Sep. 10, 1999 and U.S. Pat. Nos. 5,206,626, 5,497,140, and 5,448,110 (the disclosures of which are hereby incorporated by reference herein). However there is one environment in which it is difficult to use conventional RFID-containing devices, and that in association with metal objects. For example if no special precautions are taken and an RFID-containing label or tag is affixed to a metal object, the metal is likely to de-tune the RFID antenna. This typically is mitigated by the use of significant amounts of RF absorbing materials, or by spacing the antenna off of the metal. However if layers thick enough to properly space the RFID antenna off of the metal to which the label is affixed are utilized, then the labels are large and bulky. This reduces the efficiency of distribution and also makes printing on the device impractical using conventional printers used for printing documents.
According to the present invention a label, tag, or other composite device, is provided which overcomes the drawbacks discussed above. According to the present invention it is possible to provide a composite, such as a label or tag, that may be affixed to a metal object while substantially avoiding antenna de-tuning, but yet is not bulky or hard to handle, and can be readily imaged, including using conventional printers for imaging documents. This advantageous result is obtained according to the present invention by providing a foamable material layer of the composite (e.g. label or tag) that expands in size and reduces in density when subjected to a foaming-initiating activation. For example the foamable material layer may comprise an intumescent material, so that when heated it will decompose and/or form a gas and/or go through a phase change. Therefore after printing the layer may be subjected to heat, microwaves, or other foaming-initiating activity and then applied to a metal object, or it may be heated or otherwise activated when it is applied (such as by a self-contained pressure sensitive adhesive when in label form) to the metal object.
According to one aspect of the present invention there is provided a composite comprising: A first RFID or EAS device-containing layer. And, a foamable material layer held in proximity with the first layer, the foamable material layer expanding in size and reducing in density when subjected to foaming-initiating activation.
The foamable material layer may include an intumescent material, such as an azide compound which decomposes on heating, and/or a compound which will form a gas on heating, and/or conventional compounds that will phase change upon heating. Microwaves may also activate the foamable material, and other types of materials that foam in response to a condition may be utilized besides microwave-activated or intumescent materials.
The foamable material layer may also include RF radiation-absorbing materials, typically as fillers. A wide variety of such materials are commercially available including those shown in U.S. Pat. Nos. 5,202,688 and 5,691,667.
The composite may comprise a wide variety of other layers. For example there may be adhesive layers which operatively connect various other layers to each other. For example there may be a layer of adhesive operatively connecting the first and foamable material layers, either directly engaging both of those layers, or engaging one of the layers and an intermediate layer, or two intermediate layers. The composite also preferably comprises a printable surface layer, such as paper, on the opposite side of the first layer from the foamable material layer, and an adhesive, such as a pressure sensitive adhesive, of conventional construction, can connect the RFID device to the paper layer either directly, or through one or more intermediate layers. Also the device, especially with a printable surface layer, may be in label configuration and comprise a pressure sensitive adhesive layer operatively connected to the foamable material layer on the opposite side thereof from the first layer, either directly connected to the foamable material layer or to one or more intermediate layers. The label may be linerless, or may comprise a conventional liner of silicone coated paper or like material.
Typically indicia is imaged on the printable surface layer, and only after that imaging (e.g. in a conventional printer) is the composite subjected to the foaming-initiating activity. The pressure sensitive adhesive may adhere the composite to or adjacent a metal object, but because of the foamed layer (or multiple layers) and perhaps radiation absorbing material, especially as filler in the foamed layer, the RFID antenna will not de-tune during the operative life of the RFID.
According to another aspect of the present invention there is provided a method of utilizing an RFID, comprising: (a) Making a composite material having an RFID and at least one foamable material layer activatable by external stimuli. (b) Placing the composite in operative association with a metal object. And, (c) applying external stimuli to effect foaming of the foamable material to space the RFID from the metal object.
In the method (a) may be practiced so that the composite has a printable layer; and the method then further comprises (d) imaging the printable layer (e.g. using a conventional document printer) prior to (c). In the method (c) may be practiced before or after (b). In one embodiment the foamable material is an intumescent material, and (c) is practiced by applying heat, such as by using a hair dryer, soldering gun (that does not actually touch the composite), or a wide variety of other conventional devices. Also (a) may be further practiced by adding RF radiation-absorbing material to the foamable material as filler.
It is the primary object of the present invention to provide an easy to use, and adaptable, RFID containing composite (such as a label or tag) in association with a metal object without antenna de-tuning during the useful life of the RFID. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.